The present invention relates to an ink-jet printer for jetting or ejecting ink from a print head in order to print dots as an image and, more particularly, to an ink-jet printer in which the tone of each dot is controlled by an amount of ejected ink.
For example, Jpn. Pat. Appln. KOKAI Publication No. 10-138520 discloses a rotary drum ink-jet printer which can print a large number of pages within a short period of time. The rotary drum ink-jet printer has a rotary drum for rotating in one direction, and a print head for printing an image on a paper sheet which is wound around the rotary drum to rotate together with it. The print head has a plurality of ink-jet nozzles arranged across the paper sheet in the axial direction of the rotary drum. These ink-jet nozzles eject ink onto the paper sheet which moves relative to the print head upon rotation of the rotary drum. In this arrangement, unlike in the conventional serial ink-jet printer, the print head need not be moved across the paper sheet, so printing can be performed at a high speed.
Many ink-jet printers employ either the single-drop scheme or the multi-drop scheme. According to the single-drop scheme, each ink-jet nozzle ejects a single ink drop to print a dot. According to the multi-drop scheme, each ink-jet nozzle ejects one or more ink drops to print a dot. The tone of each dot is controlled by the volume of single ink drop in the single-drop scheme, and by the number of ink drops in the multi-drop scheme.
When ink collides against the paper sheet, it forms a dot having a diameter slightly larger than the nozzle diameter, as shown in FIG. 1. In a case where an image is formed of dots aligned at a pitch equal to the nozzle diameter, adjacent dots partially overlap. Generally, if the tones of adjacent dots are similar, they do not greatly degrade the image quality.
The amount of ejected ink increases in proportion to the tone of a dot. Each dot is influenced by the increased amount of ink if the dot is adjacent to a high-tone dot as shown in FIG. 2. More specifically, the ink flows from a certain dot to another adjacent dot depending on the ink characteristics such as viscosity, permeability, and drying speed, and the paper sheet characteristics such as water absorption properties, dryness, and thickness, and the flowed ink is sometimes observed as smear. In particular, if these dots are printed in the same color, the inks thereof have a high affinity that allows the inks to be mixed with each other more easily than with a different-color ink to integrate the dots. In most cases, ink flows from a high-tone dot to a low-tone dot. The image quality is degraded by smear of ink flowing between dots having the same color. When a dot of another color overlaps a dot having ink smear, the image quality is affected by color mixture of these dots as well. Since the ink stays in the liquid state until it is absorbed by the paper sheet rotating together with the rotary drum and dries, it sometimes flows on the paper sheet in a direction opposite to rotation of the drum. When the rotary drum rotates at a high speed, the ink may scatter around from the paper sheet. The image quality may be degraded for these reasons as well.
It is an object of the present invention to provide an ink-jet printer which can prevent degradation in quality of a multi-tone image caused by ink smear.
According to the present invention, there is provided an ink-jet printer comprising a print head for printing a plurality of dots as an image by ejecting ink onto a print medium while the print medium is moving in a predetermined direction, and a print control section which stores a plurality of dot data assigned to the plurality of dots to designate tones thereof and which drives the print head according to the plurality of dot data, wherein the print control section includes a correction section for correcting a tone of a target dot on the basis of a tone designated by dot data assigned to a dot adjacent to the target dot in the predetermined direction, in a manner so as to compensate for an ink flow due to inertia of semi-dried ink against movement of the print medium.
In this ink-jet printer, the tone of each dot is corrected on the basis of the tone designated by the dot data assigned to a dot adjacent to the dot. More specifically, this correction can selectively decrease the tones of adjacent dots which are influenced by semi-dried ink, so that quality degradation of the image due to ink smear can be prevented.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.